This program project application is submitted by the members of the Cleveland Immunopathogenesis Consortium (CLIC) a group of investigators representing 10 academic and research institutions in the United States and Canada who have engaged for more than three years in a coordinated research effort aimed at unraveling the mechanisms whereby HIV infection results in progressive immune deficiency. This group of experienced, outstanding investigators capitalizes on complementary research skills and resources and proposes an interdisciplinary program comprising 4 projects that are coordinated and supported by two cores: Administrative Core, charged with overall coordination and administration of the program and Specimen Acquisition Core, Alan Landay, PI, charged with assuring a sustained supply of clinical specimens of gut and lymph nodes to support project investigators. The projects comprise a series of interacting research platforms from basic laboratory research to experimental animal models to translational projects, each designed to explore the determinants and mechanisms whereby immune activation drives CD4+ T cell depletion and dysfunction in chronic HIV infection. Project #1: Bystander activation drives T cell losses in chronic HIV infection - PIs: Michael M. Lederman, M.D., Scott F. Sieg Ph.D. - Case, will test the hypothesis that increased systemic levels of microbial TLR ligands and common gamma chain cytokines in secondary lymphoid tissues drive central memory T cell activation and turnover in chronic HIV infection. Project #2: Loss of intestinal barrier function in HIV infection - Alan Levine, Ph.D. Case, will examine the integrity of the intestinal mucosa in HIV infection to document the mechanistic details underlying the enhanced translocation of microbial products through the damaged gut that we propose contributes to the pathogenesis of cell loss in chronic HIV infection. Project #3: Immune activation and AIDS pathogenesis in SIV-infected non-human primates - Guido Silvestri, M.D., Univ of Pennsylvania, will attempt to induce disease in non-pathogenic SIV infection of sooty mangabeys by activation of the innate immune system and will test whether blocking innate immune activation will attenuate disease pathogenesis in infected rhesus macaques. Project #4: Immune activation promotes PD1 expression and immune dysfunction in chronic HIV infection - Rafick Pierre Sekaly Ph.D. - Univ of Montreal, will examine the role of innate immune system activation through the interaction between HIV RNAs and TLR7/8 on the expression of PDL-1 and 2 and their effects on the function and survival of HIV reactive T cells. PROJECT 1: Bystander activation drives T cell losses in chronic HIV infection (Michael Lederman) PROJECT 1 DESCRIPTION (provided by applicant): Recent data from our collaborative group provide background for a new model of HIV pathogenesis that will be tested here. In this model, turnover of central memory (CM) CD4+ T cells is central to progressive cell losses of HIV infection. We propose that this is driven by interplay between indirect effects of HIV replication on the cytokine environment of secondary lymphoid tissues and in situ exposure to microbial TLR ligands translocated from the damaged gut. HIV replication is necessary but not sufficient to promote T cell turnover;microbial TLR ligands provide additional signals via two distinct mechanisms. First, they promote enhanced non-specific retention of effector CD8+ T cells in secondary lymphoid tissues by increasing expression of the C-type lectin CD69 that interferes with surface expression of sphingosine-1 phosphate receptors needed to permit exit of activated cells from lymph nodes. Sequestration of effector cells intensifies the cytokine "storm" in these tissues that results in explosive levels of common gamma chain receptor cytokines IL-2 and IL-15 that we have quantified at these sites. TLR ligands also activate CM T cells to lose characteristic resistance to death signals a resistance that is due to FOXO3a phosphorylation and inactivation. This results in heightened turnover and selective death of CM CD4+ T cells that drives the immune deficiency of HIV infection. Our aims are: 1) To characterize the intercellular interactions and mechanisms whereby selected TLR ligands and common gamma chain receptor cytokines promote activation of central memory CD4+ and CD8+ T cells. This will be achieved by detailing the specific ARC requirements for T cell activation, by exploring selected gene expression patterns for signals characteristic of cell cycle progression, apoptosis and survival and to use these results to identify the pathways that render CM T cells in HIV infection more susceptible to death signals. 2) To establish in vitro models for bystander T cell activation and sequestration after exposure to TLR ligands and common gamma chain receptor cytokines in secondary lymphoid tissues. This will be accomplished first by defining the model using peripheral blood mononuclear cells in suspension and then confirming the model in lymph node histoculture experiments. 3) To identify the proximate causes of immune activation in chronic HIV infection. We will determine the levels of selected microbial TLR agonists, HIV RNA and bacterial PGN, LPS and DNA in the plasma of chronically HIV infected persons. Based upon the results of SpAim 1 experiments, we will develop a panel of flow based reagents that will characterize the signatures of bystander T cell activation that will be applied to ex vivo analyses of blood, lymph node and gut lymphocytes in chronic HIV infection.